The present invention relates to novel methods for preparing precursors for quinoline-2,3-dicarboxylic acids. These acids are useful intermediates in the preparation of herbicidal pyridine and quinoline imidazolinone herbicidal compounds.
The herbicidal pyridine and quinoline imidazolinone compounds prepared from the present compounds include 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)quinoline-3-carboxylic acid, and esters and salts thereof and are disclosed in U.S. Pat. No. 4,638,068, incorporated herein by reference. These herbicidal imidazolinyl quinolinecarboxylic acids may be prepared by the procedure described in U.S. Pat. No. 4,518,780 (incorporated herein by reference) by cyclization, under basic conditions, with an appropriately substituted 2-carbamoyl quinoline-3-carboxylic acid, that, in turn, is prepared by the reaction of a substituted quinoline-2,3-dicarboxylic acid anhydride and appropriately substituted aminocarboxamide or aminothiocarboxamide. Quinoline-2,3-dicarboxylic acid anhydrides are readily prepared from the diacids by procedures well known in the art. However, the diacids themselves are not readily available.
Pending application for United States Letters Patent of Robert Doehner, Ser. No. 698,192 filed Feb. 4, 1985 now U.S. Pat. No. 4,656,283, describes a method useful for the preparation of quinoline-2,3-dicarboxylic acid and esters thereof by reacting a beta-anilino-alpha,betaunsaturated ester with an immonium salt (commonly called a Vilsmeier reagent). The beta-anilino-alpha, beta-unsaturated esters are obtained by the reaction of appropriately substituted anilines with keto-esters or dialkyl acetylene dicarboxylates. The overall reaction for the preparation of quinoline-2,3-dicarboxylates is illustrated in Flow Diagram I. ##STR1## wherein R' is CH.sub.3 or CO.sub.2 R" and R" is C.sub.1 -C.sub.4 alkyl, and R" is CH.sub.3 or C.sub.1 -C.sub.4 alkyl.
Where R' is CH.sub.3, the diacid is obtained by concurrent oxidation and hydrolysis of the product under aqueous basic conditions in the presence of nickel peroxide, as described in U.S. Pat. No. 4,459,409 (incorporated herein by reference).
Unfortunately, the availability of ketoesters and dialkyl acetylene dicarboxylates, such as diethyloxalacetate and diethyl acetylenedicarboxylate, is limited, thus restricting the quantities of anilinofumarate and quinoline-2,3-dicarboxylic acid, the intermediates required for preparing herbicidal 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)quinoline- 3-carboxylic acid, esters and salts thereof.
U.S. Pat. No. 4,675,432, incorporated herein by reference, describes a method for the preparation of anilinofumarates in which dichlorosuccinates are reacted with aniline in an organic solvent in the presence of aqueous base and a phase transfer catalyst in a temperature in the range of 20.degree. C. to 90.degree. C. for one to 24 hours.
Pending Application for United States Letters Patent of D. Maulding, Ser. No. 902,275, filed Aug. 29, 1986, now U.S. Pat. No. 4,766,218, describes a method for the preparation of anilinofumarates by the reaction of dichlorosuccinates with specific amines and the subsequent displacement of the amine with aniline in the presence of an organic acid.
U.S. Pat. No. 2,527,345 describes a method for the preparation of dialkyl dichlorosuccinates by introducing a stream of chlorine in intimate contact with a liquid dialkyl maleate maintained at a temperature of 25.degree. C. to 125.degree. C., at a sufficiently high rate to permit a portion of the chlorine gas to pass through the reaction mixture unreacted, in the presence of a chlorination catalyst such as ferric chloride, phosphorus pentoxide or sulfur monochloride.
Japanese patent application 71,21,564 describes an improved method for the preparation of dialkyl dichlorosuccinates by adding chlorine to a dialkyl maleate in a chlorinated hydrocarbon solvent in the presence of an alcohol, the reactions being, in general, conducted at low temperatures and in the dark.
It is an object of the present invention to provide an improved method for the preparation of dialkyl dichlorosuccinates which results in increased productivity and shorter reaction times.